Since the normal procedures for arrest do not seem to have been followed, "kidnapping" seems about the best term to describe the seizure of attorney Teng Biao (滕彪) by unknown persons in a black car without license plates. Needless to say, the probability that these are agents of the state is very high. Here's the news story from The Guardian; a statement by the Hong Kong organization China Human Rights Lawyers Concern Group is here.

The statement also mentions a contemporaneous incident in which the car of attorney Li Heping (李和平), who was recently kidnapped and severely beaten by unknown assailants (again, very probably state agents), was rammed by a police vehicle as he was taking his young son to school.